Several iterative algorithms are proposed to improve the histogram and variogram inference in the framework of the multigaussian model. The starting point is the variogram obtained after a traditional normal score transform. The subsequent step consists in simulating many sets of gaussian values with this variogram at the data locations, so that the ranking of the original values is honored. The expected gaussian transformation and the expected variogram are computed by an averaging operation over the simulated datasets. The variogram model is then updated and the procedure is repeated until convergence. Such an iterative algorithm can adapt to the case of tied data and despike the histogram. Two additional issues are also examined, referred to the modeling of the empirical transformation function and to the optimal pair weighting when computing the sample variogram. 相似文献
This study aims to validate and improve the universal evaporation duct (UED) model through a further analysis of the stability function (ψ). A large number of hydrometeorological observations obtained from a tower platform near Xisha Island of the South China Sea are employed, together with the latest variations in ψ function. Applicability of different ψ functions for specific sea areas and stratification conditions is investigated based on three objective criteria. The results show that, under unstable conditions, ψ function of Fairall et al. (1996) (i.e., Fairall96, similar for abbreviations of other function names) in general offers the best performance. However, strictly speaking, this holds true only for the stability (represented by bulk Richardson number RiB) range ?2.6 ? RiB < ?0.1; when conditions become weakly unstable (?0.1 ? RiB < ?0.01), Fairall96 offers the second best performance after Hu and Zhang (1992) (HYQ92). Conversely, for near-neutral but slightly unstable conditions (?0.01 ? RiB < 0.0), the effects of Edson04, Fairall03, Grachev00, and Fairall96 are similar, with Edson04 being the best function but offering only a weak advantage. Under stable conditions, HYQ92 is the optimal and offers a pronounced advantage, followed by the newly introduced SHEBA07 (by Grachev et al., 2007) function. Accordingly, the most favorable functions, i.e., Fairall96 and HYQ92, are incorporated into the UED model to obtain an improved version of the model. With the new functions, the mean root-mean-square (rms) errors of the modified refractivity (M), 0–5-m M slope, 5–40-m M slope, and the rms errors of evaporation duct height (EDH) are reduced by 21.65%, 9.12%, 38.79%, and 59.06%, respectively, compared to the classical Naval Postgraduate School model.
The Lorca Basin has been the object of recent research aimed at studying the phenomena of earthquake-induced landslides and its assessment in the frame of different seismic scenarios. However, it has not been until the 11th May 2011 Lorca earthquakes when it has been possible to conduct a systematic approach to the problem. In this paper we present an inventory of slope instabilities triggered by the Lorca earthquakes which comprises more than 100 cases, mainly rock and soil falls of small size (1–100 \(\hbox {m}^{3}\)). The distribution of these instabilities is here compared to two different earthquake-triggered landslide hazard maps: one considering the occurrence of the most probable earthquake for a 475-years return period in the Lorca Basin \((\hbox {M}_{\mathrm{w}}=5.0)\) based on both low- and high-resolution digital elevation model (DEM); and a second one matching the occurrence of the \(\hbox {M}_{\mathrm{w}}=5.2\) 2011 Lorca earthquake, which was performed using the higher resolution DEM. The most frequent Newmark displacements related to the slope failures triggered by the 2011 Lorca earthquakes are lower than 2 cm in both the hazard scenarios considered. Additionally, the predicted Newmark displacements were correlated to the inventory of slope instabilities to develop a probability of failure equation. The fit seems to be very good since most of the mapped slope failures are located on the higher probability areas. The probability of slope failure in the Lorca Basin for a seismic event similar to the \(\hbox {M}_{\mathrm{w}}\) 5.2 2011 Lorca earthquake can be considered as very low (0–4 %). 相似文献
We present the first winter (December to March) rainfall reconstruction based in a novel proxy, the thickness of annual calcite laminations preserved in Lake La Cruz (central–eastern Spain). A previous calibration analysis between laminae thickness and the instrumental data series (1950 to present) indicated a highly significant correlation with winter rainfall. Therefore this study attempts the winter rainfall reconstruction since the onset of laminations (1579 a.d.) by means of the calibration function previously developed. The verification analysis between inferred annual values and earlier instrumental data (1859–1949) confirms the suitability of this novel proxy and the reliability of the series reconstructed. The reconstructed series show the fluctuating character of winter rainfall in the western Mediterranean area; interdecadal dry periods alternated with wetter periods following, in a board sense, the pattern recorded by documentary sources in other regions of the Iberian Peninsula. At present times regional winter rainfall anomalies are highly correlated with the phase of the North Atlantic Oscillation (NAO). However the time series analysis showed the dominance of nonstationary components at high frequencies of the climate signal over the last four centuries suggesting that the connection between winter rainfall and the NAO has not been stable over time and also other modes of variability, not only NAO, may have conditioned winter rainfall variability. 相似文献
